Chapter 7:  The Cell

Cell: basic unit of living organism.  We have smaller units, but

 they are organized and packaged in cells.

Microscopes

van Leeuwenhoek:  Invented the simple light microscope. 

                                1 lens, used natural light.

Compound light microscopes- use series of lenses to magnify

sample in steps (up to 1500x)

-have gotten more sophisticated- confocal &

        fluorescence

Electron Microscope (1940s)- 500 000x magnification enables

us to visualize structures within a  cell

        Scanning EM: scan the surface (3D)

        Transmission EM: looks within a cell

        Scanning Tunneling Microscope: looks at atoms

Read "Focus on microscopes" p 178

The Cell Theory

Robert Hoeke: studied cork (dead cells of oak bark) and saw

small geometric shapes.  Named them cells b/c they looked like a series of small rooms.

Matthais Schleiden (1830s)- plants are made of cells

Theodore Schwann (1830s)- animals are made of cells

The Theory:

1.  All organisms are composed of > 1 cell

2.  The cell is the basic unit of organization of all org.

3.  All cells come from pre-existing cells = division

Two Cell Types

Prokaryotes: lack internal, membrane bound organelles

Eukaryotes: cells are compartmentalized into membrane bound

        organelles, each with specific function.

Organelles: membrane bound structures with specific functions-

        facilitate chemical reactions that require conditions other

        than those found in the cell

Robert Brown/Rudolf Virchow- the nucleus manages cell

function

The Plasma Membrane

Boundary between cell and environment

Enables cell to regulate internal environment

Allows just enough of the good stuff (glucose, amino acids, lipids

        in and keeps the bad out

Lets waste and excess out

homeostasis: helps maintain balance

All these are made possible by: selective permeability- allows

        some but not all in (bouncer at the door, screen in a

window)

Water enters freely, ions are regulated

Structure of the Plasma Membrane

Phospholipid bilayer- 2 layers of lipids that are tipped with

phosphate groups.

Makes lipids polar- lipids on inside b/c they don't like water

                phosphates on exterior so cell can interact with water

Water soluble molc

                                                                        don't move thru

                                                                        freely b/c lipids stop

                                                                        them

Fluid mosaic model:  membrane is flexible, component flow

                        lipids are like a lake

                        proteins are like boats, decks above, hulls below

Other components:

        cholesterol: stabilizes membrane, prevents fatty acids

                                from sticking together

        Proteins: some span whole membrane, some don't

                        transport proteins direct selective permeability

        Proteins and Carbos on surface responsible for cell ID

       Proteins on inner surface: structure, attach to cytoskeleton

Cell Structure

Cell Walls

Plant cells, fungi

Rigid structure outside plasma membrane provides

additional support and structure- defines shape. 

        Not selective

Nucleus

        contains DNA- the blueprint for proteins

        proteins do EVERYTHING- therefore, nucleus is in control

        chromatin: strands of DNA- makes up chromosomes

        nucleolus: makes ribosomes in nucleus

        ribosomes: site of protein synthesis in cytoplasm

        nuclear membrane: phospholipid bilayer with pores for

transport.  Barrier between nucleus and cytoplasm

        Cytoplasm: gel that fills cells, suspends organelles

DNA ----------> RNA -----------------------> cytoplasm

Endoplasmic Reticulum

        cellular chemical reactions- folds and modifies proteins

(lipid anchors)

        series of highly folded membranes continuous with nuclear

                membrane

        Ribosomes attach to ER (rough ER) for protein syn.

        SER- smooth ER, no ribosomes

                RER: syn protein and thread thru & into ER

                SER: syn. cytoplasmic proteins, lipid production

                                and storage

Golgi Complex/Apparatus

        modifies proteins (adds carbohydrates to proteins)

        flat, tubular membranes

Vesicles

        Carry proteins and lipids from ER--> Golgi-->organelles/PM\

        Similar to the post office, organizing and delivering mail

Vacuoles

        temporary storage of materials: food, enzymes, waste

        plants: 1 huge vacuole

        animals: series of small vacuoles

Lysosomes

        contain digestive enzymes

        excess or worn out organelles, bacteria, viruses

        can fuse with vacuole to digest contents

        can digest whole cells: tadpole's tail: apoptosis, necrosis

Energy

Chloroplasts

capture light, photosynthesize

        double membrane

        inner "thylakoid membrane" traps light

                stack to form grana

                surrounded by stroma- fluid

Plastids

 plant storage- starches, lipids, pigment

        chlorophyll- green pigment in chloroplasts

Mitochondria

        transform energy for the cell

        double membrane- inner memb, energy storage

Support and Locomotion

 b

Cells aren't just sac of stuff

Cytoskeleton- rods an filaments = framework and transport

system- constantly changing

        microtubules: thin, hollow protein fibers

        microfilaments: thin solid protein fibers

                scaffold, support, shape

Cilia and Flagella

        composed of microtubule pairs surrounded by PM

        cilia- short hair-like, numerous, wavelike motion

        flagella- long whiplike